-LRB- CNN -RRB- -- Dozens of whales are dead after they got stuck on a remote beach in New Zealand , authorities said Monday .

The 39 long-finned pilot whales became stranded overnight on Farewell Spit , a narrow claw of land that juts out into the sea from the northern tip of New Zealand 's South Island .

Twelve of the whales had died by the time they were found Monday morning . Conservation officials said they decided to euthanize the remaining 27 because the chances of getting them safely back out to sea were too slim .

`` They have come very high onto the beach in a big tide , '' said John Mason , the conservation services manager for the area where the whales were found . `` The big tides are now reducing , coming in further out from shore , so it would be difficult to get the large animals into deep enough water to refloat them . ''

He said that he and his staff had `` carefully weighed up the likelihood of being able to refloat '' the whales , but that they `` determined that due to various factors it was unlikely they could be rescued . ''

`` Rather than prolong the suffering of the remaining 27 whales , we decided to humanely euthanize them , '' he said in a statement .

Surrounded by oceans rich in marine life , New Zealand has one of the highest stranding rates for sea mammals in the world .

An average of about 300 dolphins and whales get stuck on the country 's coasts each year , according to Project Jonah , a nonprofit group that aims to rescue and protect marine mammals .

Golden Bay , the area where the group of pilot whales got stuck , is known as a stranding hotspot because of its protruding coastline , gently sloping beaches and system of currents .

Pilot whales , which live offshore , are among the most vulnerable species to mass strandings in such conditions , according to the Encyclopedia of New Zealand .

But the number of whales that died on Farewell Spit this week pales in comparison with some of New Zealand 's worst strandings .

In 1998 , more than 300 pilot whales died after they got stuck in Doughboy Bay on Stewart Island , which sits off the south coast of the South Island .

New Zealand 's worst ever stranding took place in 1918 , the Encyclopedia of New Zealand says , when around 1,000 pilot whales got marooned on Long Beach in the Chatham Islands , which are situated hundreds of kilometers off the country 's east coast .

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CNN 's Khushbu Shah contributed to this report .

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The group of whales got stranded overnight on New Zealand 's South Island

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Twelve had died by the morning and officials decided to euthanize 27 others

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`` It was unlikely they could be rescued , '' a local conservation official says

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New Zealand has one of the highest stranding rates for marine mammals